This invention relates to contact arrangements for vacuum switches in general and more particularly to a contact arrangement with contacts which are disposed coaxially with respect each other, each contact containing a contact carrier provided with slots, and a central support body of electrically poorly conducting material.
The maximum interrupting capacity of vacuum switches is determined, as is well known, by the maximum permissable values of current during the arcing phase and the returning voltage after the arc is interrupted, and can be influenced favorably by a magnetic field parallel to the direction of the arc current. A contraction of the arc, which leads to an increase of the arc voltage and the power conversion associated with this voltage, can be prevented by a coaxial magnetic field in the region of the arc between the opened contacts. For this purpose a coil cylindrically surrounding the switching chamber can be provided in the case of what are known as axial field contacts. The coil is electrically connected in series with the switch contacts and builds up an axial magnetic field which depends on the current. The magnetic field extends through the gap between the coaxial contacts in the axial direction. To increase the field strength in the contact gap, the coil may also be constructed with two layers and the turns can be designed going forward and backward in helical fashion. The manufacture of such vacuum switches, however, is relatively expensive (DE-OS No. 29 11 706 ).
Hollow contacts, the central contact area of which is concentrically surrounded by an arc running area are also known in the art. The current input is connected to the central contact surface as well as to the outer rim of the arc running surface in such a manner that an annular cavity is generated. The central contact surface is separated from the arc running surface by an annular gap. The object of this design is to avoid uneven burn-off of the contact surfaces by exerting magnetic forces alternatingly acting radially outward and inward on the arc (DE-AS No. 23 52 540).
A contact arrangement for vacuum switches with radial field contacts in which, after the contacts between the annular contact surfaces are opened, an arc which is supposed to rotate between the contacts by azimuthal magnetic forces is drawn is also known. For this purpose, the contact carriers of cup contacts which are arranged coaxially with respect to each other, are provided with slots extending in opposite directions. With this contact shape, a magnetic field which is oriented substantially perpendicular to the axis of the contacts and thereby, perpendicular to the arc is obtained between the opened contacts. With a special design of the contact arrangement, the strength of the magnetic field and, thereby, the velocity of motion of the arc can further be increased by arranging a core of ferromagnetic material with the hollow cylindrical contact carrier (DE-AS No. 11 96 751).
It is now an object of the present invention to provide a contact arrangement with axial field contacts which generate a flux density between the opened contacts such that contraction of the arc and thereby, thermal overload, particularly of the respective anode is prevented and the switching capacity is increased accordingly. At the same time, the contacts should have low resistance and inductance, and should be insensitive to high contact pressure in the closed condition of the vacuum switch.